Pivots come with the frame but you most likely will need the shock mounting bushings that are the correct size for the frame. RWB has needle bearings you could also choose but are much more expensive.
Nothing wrong with going up to 120mm travel front fork, specs say the rear travel is 110mm.
Don't have XLoc but I do recommend getting remote lockouts on the suspension, my Fox fork & shock both have three positions (CTD) and the Scott dual lock lever I installed works really well,
DT Swiss makes nice hubs, 350's are a better value than the 240's but if you want the best it always costs more. Bitex 401 hubs are also a good choice that I went with on my carbon wheels, but if I had it to do again I'd go with DT Swiss.
I think my XX1 build was right around $3400 so it looks like you are on the right track.